Relaxation properties of the quantum kinetics of carrier-LO-phonon interaction in quantum wells and quantum dots

The time evolution of optically excited carriers in semiconductor quantum wells and quantum dots is analyzed for their interaction with LO phonons. Both the full two-time Green's function formalism and the one-time approximation provided by the generalized Kadanoff-Baym ansatz are considered, in order to compare their description of relaxation processes. It is shown that the two-time quantum kinetics leads to thermalization in all the examined cases, which is not the case for the one-time approach in the intermediate-coupling regime, even though it provides convergence to a steady state. The thermalization criterion used is the Kubo-Martin-Schwinger condition.